The Ikaria high-temperature Metamorphic Core Complex (Cyclades, Greece): Geometry, kinematics and thermal structure Alexandre Beaudoin, Romain Augier, Valentin Laurent, Laurent Jolivet, Abdeltif Lahfid, Valérie Bosse, Laurent Arbaret, Aurélien Rabillard, Armel Menant To cite this version: Alexandre Beaudoin, Romain Augier, Valentin Laurent, Laurent Jolivet, Abdeltif Lahfid, et al.. The Ikaria high-temperature Metamorphic Core Complex (Cyclades, Greece): Geometry, kinematics and thermal structure. Journal of Geodynamics, Elsevier, 2015, 92, pp.18-41. 10.1016/j.jog.2015.09.004. insu-01225362 HAL Id: insu-01225362 https://hal-insu.archives-ouvertes.fr/insu-01225362 Submitted on 6 Nov 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. 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Distributed under a Creative Commons Attribution - NoDerivatives| 4.0 International License Accepted Manuscript Title: The Ikaria high-temperature Metamorphic Core Complex (Cyclades, Greece): Geometry, kinematics and thermal structure Author: Alexandre Beaudoin Romain Augier Valentin Laurent Laurent Jolivet Abdeltif Lahfid Valerie´ Bosse Laurent Arbaret Aurelien´ Rabillard Armel Menant PII: S0264-3707(15)30025-9 DOI: http://dx.doi.org/doi:10.1016/j.jog.2015.09.004 Reference: GEOD 1390 To appear in: Journal of Geodynamics Received date: 29-1-2015 Revised date: 18-9-2015 Accepted date: 28-9-2015 Please cite this article as: Beaudoin, A., Augier, R., Laurent, V., Jolivet, L., Lahfid, A., Bosse, V., Arbaret, L., Rabillard, A., Menant, A.,The Ikaria high-temperature Metamorphic Core Complex (Cyclades, Greece): Geometry, kinematics and thermal structure, Journal of Geodynamics (2015), http://dx.doi.org/10.1016/j.jog.2015.09.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. *Highlights (for review) Ikaria Island corresponds to a large-scale migmatite-cored MCC. Thermal structure revealed by RSCM shows a drastic increase from top to bottom. The MCC was exhumed by two detachments through the brittle-ductile transition. Migmatites were dated to 15.7 ± 2 Ma by U-Th-Pb analysis on monazites. A large-scale high temperature zone is proposed for the central part of the Aegean. Accepted Manuscript Page 1 of 86 *Manuscript Click here to view linked References 1 The Ikaria high-temperature Metamorphic Core Complex (Cyclades, Greece): Geometry, 2 kinematics and thermal structure. 3 4 Alexandre Beaudoina,b,c,*, Romain Augiera,b,c, Valentin Laurenta,b,c, Laurent Joliveta,b,c, 5 Abdeltif Lahfidb,c, Valérie Bossed, Laurent Arbareta,b,c, Aurélien Rabillarda,b,c, Armel 6 Menanta,b,c 7 8 aUniversité d’Orléans, ISTO, UMR 7327, 45071, Orléans, France 9 bCNRS/INSU, ISTO, UMR 7327, 45071 Orléans, France 10 cBRGM, ISTO, UMR 7327, 45060 Orléans, France 11 dUniversité Blaise Pascal, Laboratoire Magmas & Volcans, CNRS, UMR 6524, 63000, 12 Clermont-Ferrand, France 13 14 *Corresponding author: Alexandre Beaudoin, ISTO, 1A rue de la Férollerie, 45071, Orléans, 15 France (e-mail: [email protected]; Tel: +33 2 38 49 25 73) 16 17 18 Abstract 19 20 This work attempted at clarifying the structure of Ikaria using primarily intensive 21 geological mappingAccepted combined with structural analysis Manuscript and a geothermometry approach of 22 Raman spectrometry of carbonaceous material. Foliation over the whole island defines a 23 structural dome cored by high-grade to partially-molten rocks. Its exhumation was completed 24 by two top-to-the-N ductile extensional shear zones, operating in the ductile and then the 25 brittle fields, through a single extensional event coeval with progressive strain localization. Page 2 of 86 26 The thermal structure of the dome with regard to position of ductile shear zones was retrieved 27 using the Raman spectroscopy of carbonaceous material. Peak-metamorphic temperatures 28 range from 390 °C in the upper parts of the structure down to 625 °C in the core of the dome 29 in the vicinity of migmatites and S-type granite. Pioneer in situ U-Th-Pb analyses on monazite 30 performed on the leucosome parts of these rock yielded a 15.7 ± 0.2 Ma age. Ikaria Island 31 thus completes the series of Miocene migmatite-cored Metamorphic Core Complex in the 32 central part of the Aegean domain where a genuine high-temperature zone can be defined as 33 the central Aegean HT zone. There, the extreme stretching of the continental crust is 34 associated with dominantly top-to-the-N kinematics. 35 36 Keywords: Structural analysis; RSCM geothermometry; U-Th-Pb geochronology; 37 Metamorphic Core Complex; Ikaria; North Cycladic Detachment System. 38 39 40 1. Introduction 41 42 In the Mediterranean realm, the retreat of oceanic slabs triggered the initiation of back- 43 arc extension (i.e large-scale extension in the upper plate of a subduction zone), leading to the 44 collapse of previously thickened continental lithosphere (Le Pichon and Angelier, 1979; 45 Malinverno and Ryan, 1986; Dewey, 1988; Platt and Vissers, 1989; Royden, 1993; Jolivet 46 and Faccenna, 2000;Accepted Rosenbaum et al., 2002; Faccenna Manuscript et al., 2004; Jolivet et al., 2008). This 47 post-orogenic evolution (i.e. crustal thinning by extension-related normal faulting after an 48 episode of crustal thickening) resulted in the formation of series of extensional domains or 49 wide-rift systems (Lister et al., 1984; Buick, 1991; Corti et al., 2003) such as the Alboran Sea, 50 the Tyrrhenian Sea, the Pannonian Basin and the Aegean Sea. Lateral evolution from the Page 3 of 86 51 central parts of the extensional domains to the bounding non-collapsed orogenic segments 52 implies drastic lateral gradients of finite extension and suggests highly non-cylindrical 53 structures. In the Aegean Sea, along with the drastic decrease in topography and crustal 54 thickness, the main orogenic structures of the Hellenic belt are increasingly reworked by 55 extension from continental Greece to Naxos, in the center of the Aegean Sea. Extensional 56 structures related to back-arc crustal stretching evolve from essentially brittle steep and 57 shallow-dipping normal faults in continental Greece to shallow-dipping ductile shear zones in 58 the center of the Aegean domain (Jolivet and Patriat, 1999; Jolivet et al., 2010). Furthermore, 59 a straightforward correlation between the degree of non-coaxiality of the back-arc domain and 60 the amount of stretching of the continental crust is observed at the scale of the entire Aegean 61 domain (e.g. Augier et al., 2015). Marginal areas that connect to non-collapsed orogenic 62 segments display symmetrically arranged detachment systems. In the western parts of the 63 Aegean domain, both the West Cycladic Detachment System (WCDS) and the North Cycladic 64 Detachment System (NCDS) exhume a horst-shaped domain, where orogenic features are still 65 nicely preserved, depicting bivergent extension (e.g. Jolivet et al., 2010; Grasemann et al., 66 2012). Conversely, in the center of the Aegean domain, deformation remains highly 67 asymmetric from Mykonos in the north, all the way to Sikinos in the south (e.g. Gautier et al., 68 1993; Kumerics et al., 2005; Denèle et al., 2011; Augier et al., 2015). There, orogenic features 69 are particularly overprinted or even locally erased by the combined effects of intense top-to- 70 the-N shearing and partial-melting. Migmatite-cored Metamorphic Core Complexes (MCCs), 71 associated with AcceptedMiocene intrusions, roofed by major Manuscript top-to-the-N crustal-scale detachments, 72 are described on Naxos, in the center (e.g. Lister et al., 1984; Urai et al., 1990; Buick, 1991; 73 Gautier and Brun, 1994; Jolivet et al., 2004a; Vanderhaeghe, 2004) and Mykonos in the north 74 of the Aegean domain (Lecomte et al., 2010; Denèle et al., 2011). Concentrating a large part 75 of the total amount of stretching, recognition of MCCs therefore appears of prime importance. Page 4 of 86 76 Similarly, asymmetry of crustal thinning at the regional-scale is another key-question for 77 understanding back-arc extension dynamics. However, the current understanding of back-arc 78 dynamics in the Aegean domain is hindered by the severe lack of knowledge for the bulk of 79 its eastern part. 80 One of the largest Aegean islands, displaying the largest intrusion of the Aegean Sea, 81 located between the northern Cyclades and western Turkey, Ikaria Island has been the focus 82 of several recent studies. However, the first order structural architecture of this island remains 83 conflicting and the existing geological maps of Ikaria present marked discrepancies. Besides, 84 the current knowledge of the metamorphic record and particularly the thermal structure of 85 Ikaria remain fragmentary. These problems were reconsidered after an extensive field survey, 86 including primarily new geological mapping and structural analysis. The position and 87 importance of the various tectonic contacts as well as the bulk thermal architecture of the 88 island were further constrained using the geothermometry approach of Raman Spectrometry 89 of Carbonaceous Material (RSCM). Following their recent discovery, the migmatites 90 described in the core of the structure were dated by U-Th-Pb LA-ICPMS analyses on 91 monazite.